1. Technical Field
The present invention relates to a medium detection mechanism, a medium detection method, and a printing apparatus including a medium detection mechanism.
2. Related Art
A medium detection mechanism has been known which detects a medium by using an optical sensor including an irradiation section that emits light and a light receiving section that receives light in a printing apparatus such as a printer. In the medium detection mechanism, irradiation light is irradiated from the irradiation section, reflected light that is reflected by the medium or a surface of a medium guide that holds the medium is received by the light receiving section, and the presence or absence of the medium is detected by using the amount of received light. JP-A-2009-263126 discloses an image forming apparatus including an image reading apparatus (a medium detection mechanism) that detects the presence of a document (a medium). In the image reading apparatus, emboss processing is applied to a surface by which light emitted from a light emitting section is reflected, and detection accuracy of a document is improved by reducing the reflected light that goes to a light receiving section when there is no document.
However, the medium detection mechanism described in JP-A-2009-263126 is assumed to be used in a scanner section of a copy machine or the like into which no external light enters. When the medium detection mechanism is provided to, for example, a medium supply mechanism of a printing apparatus including an automatic sheet feeder exposed to outside, reflected light of external light such as illumination reaches a light receiving section of an optical sensor and detection accuracy of a medium on which an image or the like will be printed decreases, so that there is a problem that it is erroneously determined that there is a medium even though no medium is held by a medium guide.